The 'free board' in an irrigation canal is provided to:
Choose the correct answer
Increase canal discharge capacity
Safety margin above FSL for waves, floods, uncertainty — prevents overtopping of canal banks
Allow fish to jump out of canal
Reduce seepage losses
Correct Answer
B. Safety margin above FSL for waves, floods, uncertainty — prevents overtopping of canal banks
Why is this the answer?
Freeboard: vertical distance between the Full Supply Level (FSL) and top of bank. Provided for: (1) Wave action in wind; (2) Measurement uncertainty; (3) Excess inflow during floods; (4) Unexpected blockages downstream raising level. Typical freeboard: 0.5–1.0 m for large canals; 0.3–0.5 m for small channels. IS 7112 recommends freeboard based on discharge.
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